DIRECTIONSCombine the soy sauce, canola oil, lemon zest, lemon juice, ginger root, garlic and mustard in a bowl. Pour half the sauce in a low flat dish, large enough to hold the tuna steaks in a single layer. Place the tuna on top of the sauce and spread the remaining sauce on top. Cover with plastic wrap and refrigerate for at least 4 hours or preferable overnight.Thirty minutes before you are ready to serve, preheat a gas grill.When the coals are medium-hot, brush the cooking grates with oil to prevent the fish from sticking. Remove the fish from the marinade, allowing some of the ginger to cling to the fish and discard the marinade. Sprinkle the fish generously on both sides with salt and place it over the coals. Cook 5 minutes on each side, just until it is no longer pink in the middle. Place on a platter, cover tightly with foil and allow it to rest 10 to 15 minutes. Serves 6.